Centrifugal blower

ABSTRACT

A centrifugal multi-blade fan has multiple blades about a rotational shaft and draws in air along the rotational shaft and then blows the air approximately perpendicular to the rotational shaft to reduce wind noise. A scroll casing encloses the multi-blade fan and defines a scroll-shaped airflow passage for directing the air blown from the multi-blade fan. The scroll casing has an intake opening and an outlet opening at a scroll end, in a downstream scroll casing portion. The scroll casing expands such that a flow passage cross-sectional area on the airflow downstream side is larger than that on an airflow upstream side. A ratio of a blade length to a diameter of the multi-blade fan is greater than or equal to 0.12, and an outer scroll casing radius, relative to the rotational axis, increases as a logarithmic spiral, its expansion angle being from 3.3° to 4.8°.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/888,080 filed Jul. 31, 2007 which is a divisional of U.S. patentapplication Ser. No. 10/192,131 filed on Jul. 10, 2002. This applicationis based upon, claims the benefit of priority of Japanese PatentApplications No. 2001-215649 filed Jul. 16, 2001, and No. 2001-322201filed Oct. 19, 2001. All of the above referenced U.S. and Japanesepatent applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal blower having acentrifugal multiblade fan (abbreviated as a centrifugal fan hereafter)applied to a vehicular air-conditioning apparatus.

2. Description of the Related Art

Generally, centrifugal fans use a centrifugal force to take in air in anaxial direction, and to blow the air outward in a radial direction. Theair blown out from the centrifugal fan has an airflow of an axialdirection component directed from an intake side to a counter-intakeside.

In the invention disclosed in Japanese Patent Laid-Open Publication No.Hei. 5-195995, an expanded part for expanding an airflow passage on thecounter-intake side is formed in the airflow passage outside acentrifugal fan, and a side wall on a side of the centrifugal fan istilted as a tilted surface in the expanded part (See FIGS. 20A and 20B).FIG. 20B is an enlargement of the area noted by the circular portion XXBof FIG. 20A. With this construction, the air blown out from thecentrifugal fan flows smoothly along the tilted surface as shown as asolid line in FIG. 20B, and generation of airflow flowing toward theinlet opening along the inner wall surface on the outer peripheral sideis restrained. As a result, interference (collision) of air directlyflowing from the centrifugal fan toward the inner wall surface on theouter peripheral side of the scroll casing, air blown outward in theradial direction, and the air flowing toward the inlet opening along theinner wall surface on the outer periphery side is prevented fromreducing wind noise.

The inventors produced and examined the blower described in thepublication above, investigated the flow of the air in detail, and foundthe following points.

When the quantity of the airflow blown out from the centrifugal fan isrelatively large, the air flows as described above (the solid line inFIG. 20B) and a stable swirling flow is generated. When the quantity ofthe airflow blown out from the centrifugal fan is relatively small, thequantity of the airflow is not enough for air which has collided with awall surface 74 f to flow along a wall surface 74 g and a tilted surface74 h. Therefore, the flow does not extend over the entire expanded part,and a stable swirling flow is not generated. As a result, the flowbecomes unstable, the airflow tends to be disturbed, and wind noisebecomes worse.

SUMMARY OF THE INVENTION

In view of the foregoing problems, an object of the present invention isto provide a centrifugal blower which can sufficiently reduce the windnoise even when the airflow quantity is small.

To attain the above object, a centrifugal blower according to a firstaspect of the present invention comprises a centrifugal multiblade fanprovided with multiple blades about a rotational shaft for taking in airin an axial direction of the rotational shaft and blowing the airoutward in a radial direction with respect to the rotational shaft. Ascroll casing is used for storing the centrifugal multiblade fan, thescroll casing constituting a scroll-shaped airflow passage forchanneling the air blown out from the centrifugal multiblade fan, andhaving an intake opening on one end in the axial direction of therotational shaft, and an outlet opening on an airflow downstream side ofa scroll end.

The centrifugal blower is characterized in that expanded parts, expandedin a direction parallel with the rotational shaft, are provided in theairflow passage such that a flow passage cross-sectional area on theairflow downstream side is larger than that on the airflow upstreamside. Additionally, a ratio of a blade length of the blades to adiameter of the centrifugal multiblade fan is 0.12 and over, an outerperipheral radius of the scroll casing extends as a logarithmic spiral,and its expansion angle n is from 3.3° to 4.8°.

With this construction, noise is sufficiently reduced even when theairflow quantity is small as shown in FIGS. 8 and 9 as described below.

A centrifugal blower according to a second aspect of the presentinvention comprises a centrifugal multiblade fan provided with multipleblades about a rotational shaft for taking in air along an axialdirection of the rotational shaft, and blowing the air outward in aradial direction. Additional components include a scroll casing forstoring the centrifugal multi-blade fan, the casing constituting ascroll-shaped airflow passage for the air blown out from the centrifugalmultiblade fan. Also evident are an intake-opening on one end in theaxial direction of the rotational shaft, and an outlet opening on theairflow downstream side of the scroll end. This centrifugal blower ischaracterized in that expanded parts, expanded in a direction parallelwith the rotational shaft, are provided in the airflow passage such thata flow passage cross-sectional area on the airflow downstream side islarger than that on the airflow upstream side, a ratio of a blade lengthof the blades to a diameter of the centrifugal multiblade fan is 0.12 orabove, an outer peripheral radius of the scroll casing extends as alogarithmic spiral, and its expansion angle is from 3.5° to 4.5°.

With this construction, airflow noise is sufficiently reduced even whenthe airflow quantity is small as shown in FIGS. 8 and 9 described below.

A dimension of the winding-end portion in the direction parallel withthe rotational shaft is 1.1 times to 2.3 times a dimension of a nose inthe scroll casing in the direction parallel with the rotational shaft ina third aspect of the invention. With this constitution, noise issufficiently reduced even when the airflow quantity is small as shown inFIGS. 8 and 10 described below.

The dimension of the winding-end portion in the direction parallel withthe rotational shaft is from 1.3 times to 2.1 times of the dimension ofa nose in the scroll casing in the direction parallel with therotational shaft in a fourth aspect of the invention. With thisconstitution, noise is sufficiently reduced even when the airflowquantity is small as shown in FIGS. 8 and 10 described below.

The airflow passage may be constituted so as to have an approximatelyrectangular cross-section in a fifth aspect of the invention. Theairflow passage is constituted so as to have an approximatelyrectangular cross-section whose corners are formed as an arc (roundedinternal corners) in a sixth aspect of the invention. With thisconstitution, since an unstable swirling flow is prevented from beinggenerated at the corners in the airflow passage, and simultaneously, agenerated swirling flow is circulated smoothly, the swirling flow isstabilized, and the noise is reduced.

A protrusion protruding toward the centrifugal multiblade fan isprovided on the inner wall on the outer periphery of the scroll casing,and has an approximately triangular shape protruding toward thecentrifugal multi-blade fan as seen from a primary flow direction of theair flowing through the airflow passage in a seventh aspect of theinvention.

When the protrusion is provided at a part with which air with thehighest flow rate of the air blown out from the centrifugal multibladefan collides, the air blown out from the centrifugal multiblade fan iseasily split into the inlet opening side and the outlet opening side. Asa result, generation of a swirling flow is promoted, and wind noise isreduced.

A centrifugal blower according to an eighth aspect of the presentinvention comprises a centrifugal multiblade fan provided with multipleblades about a rotational shaft for taking in air along an axialdirection of the rotational shaft, and for blowing the air outward in aradial direction. The blower also exhibits a scroll casing for storingthe centrifugal multi-blade fan, constituting a scroll-shaped airflowpassage for channeling and directing the air blown away from thecentrifugal multi-blade fan. The blower has an intake opening on one endin the axial direction of the rotational shaft, and an outlet opening onan airflow downstream side of a scroll end. The centrifugal blower ischaracterized in that a ratio of a blade length of the blades to adiameter of the centrifugal multi-blade fan is 0.12 and over, a faninlet opening angle of the centrifugal multi-blade fan is from 55° to85°, a fan outlet opening angle of the centrifugal multi-blade fan isfrom 15° to 45°, and a fan advancing angle, which is an angle between aline connecting an inlet-opening-side end of the blade with therotational center of the multiblade fan, and a line connecting an outletopening end of the blade with the rotational center of the multi-bladefan, ranges from 4° to 10°. With this construction, noise issufficiently reduced even when the airflow quantity is small as shown inFIGS. 16 to 19 described below.

It is preferable that a curvature radius of the blade on the inletopening side is equal to or less than a curvature radius of the blade onthe outlet opening side in a ninth aspect of the invention.

It is preferable that the blades have a shape for smoothly connectingcurved surfaces having two or more curvature radii with one another in atenth aspect of the invention.

An outer peripheral side radius of the scroll casing extends as alogarithmic spiral, and its expansion angle n is from 3.3° to 4.8° in aneleventh aspect of the invention.

With this constitution, noise is sufficiently reduced even when theairflow quantity is small as shown in FIG. 8, FIG. 9, and FIGS. 16 to 19described below.

The outer peripheral radius of the scroll casing extends as alogarithmic spiral, and its expansion angle n is from 3.5° to 4.5° in atwelfth aspect of the invention.

With this constitution, noise is sufficiently reduced even when theairflow quantity is small as shown in FIG. 8, FIG. 9, and FIGS. 16 to 19described below.

It is preferable that expanded parts, expanded in a direction parallelwith the rotational shaft, are provided in the airflow passage such thata flow passage cross-sectional area on the airflow downstream side islarger than that on the airflow upstream side in a thirteenth aspect ofthe invention.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of an air-conditioning apparatus accordingto embodiments of the present invention;

FIG. 2 is a sectional view of a blower according to a first embodimentof the present invention;

FIG. 3 is a descriptive drawing for an outlet-opening angle β2;

FIG. 4 is a view seen from a direction indicated by an arrow A in FIG.2;

FIG. 5 is a view seen from a direction indicated by an arrow B in FIG.2;

FIG. 6A is a descriptive drawing for describing an air flowing effect ofthe present invention;

FIG. 6B is a descriptive drawing for describing an air flowing effect ofthe present invention;

FIG. 7 is a schematic drawing showing airflow in an airflow passage of ascroll casing;

FIG. 8 is a graph showing a relationship between specific noise leveland blade length divided by fan diameter (L/D);

FIG. 9 is a graph showing a relationship between the specific noiselevel and an expansion angle;

FIG. 10 is a graph showing a relationship between the specific noiselevel and an expansion ratio in an axial direction;

FIG. 11 is a schematic drawing showing a sectional shape of an airflowpassage according to a second embodiment of the present invention;

FIG. 12 is a schematic drawing showing a sectional shape of an airflowpassage according to a third embodiment of the present invention;

FIG. 13 is a descriptive drawing showing an inlet-opening angle β1, anoutlet-opening angle β2, and an advancing angle γ;

FIG. 14A is a descriptive drawing showing a relationship between theinlet-opening angle β1, the outlet-opening angle β2, the advancing angleγ, and airflow;

FIG. 14B is a descriptive drawing showing a relationship between theinlet-opening angle β1, the outlet-opening angle β2, the advancing angleγ, and airflow;

FIG. 15A is a descriptive drawing showing a relationship between theinlet-opening angle β1, the outlet-opening angle β2, the advancing angleγ, and the airflow;

FIG. 15B is a descriptive drawing showing a relationship between a largeblade length and airflow;

FIG. 16 is a chart showing a relationship between the minimum specificnoise level, the ratio of blade length to fan diameter L/D, and theairflow rate;

FIG. 17 is a chart showing a relationship between the fan inlet-openingangle β1, the specific noise level, and the airflow rate;

FIG. 18 is a chart showing a relationship between the fan outlet-openingangle β2, and the specific noise level; and a relationship between thefan-outlet-opening angle β2 and the airflow quantity;

FIG. 19 is a chart showing a relationship between the advancing angle γand the specific noise level; and a relationship between the advancingangle γ and the airflow quantity; and

FIG. 20A is a perspective view of a blower according to the prior art;and

FIG. 20B is an enlarged view of encircled area XXB in FIG. 20A accordingto the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT First Embodiment

A centrifugal blower is applied to a blower in a vehicleair-conditioning apparatus according to a first embodiment of thepresent invention. FIG. 1 is a schematic drawing of a vehicleair-conditioning apparatus 1 for a vehicle equipped with a water-cooledengine, and the centrifugal blower (abbreviated as a blower hereafter)according to the present invention.

An internal air intake opening 3 for taking in cabin air, and anexternal air intake opening 4 for taking in outside air are formed on anairflow upstream side of an air conditioner casing 2 forming an airflowpassage. An intake-opening switching door 5 is provided for selectivelyopening and closing the intake openings 3 and 4. Drive means such as aservomotor, or manual operation opens and closes the intake-openingswitching door 5.

A filter (not shown) for removing dust in the air, and a blower 7according to the present invention are provided on the airflowdownstream side of the intake-opening switching door 5. The blower 7blows air drawn from both of the intake openings 3 and 4 to theindividual outlet openings 14, 15, and 17 which will be described later.

An evaporator 9 for cooling the air blown out into a cabin is providedon the airflow downstream side of the blower 7, and the entire volume ofair blown by the blower 7 passes through the evaporator 9. A heater core10 for heating the air blown out into the cabin is provided on theairflow downstream side of the evaporator 9, and this heater core 10uses the coolant for the engine 11 as a heat source to heat the air. Theblower shown in FIG. 1 is a schematic drawing, and its detail will bedescribed later.

A bypass passage 12 for bypassing the heater core 10 is formed in theair conditioner casing 2. An air mix door 13 for adjusting an airflowquantity ratio between an airflow quantity passing through the heatercore 10, and an airflow quantity passing through the bypass passage 12to adjust the temperature of the air blown into the cabin, is providedon the airflow upstream side of the heater core 10.

A face aperture 14 for blowing out the air-conditioned air to the upperbody of passengers in the cabin, a foot aperture 15 for blowing out theair to the feet of the passengers in the cabin, and a defroster aperture17 for blowing out the air on the inner surface of a windshield 16 areformed on an extreme airflow downstream side of the air conditionercasing 2.

Blow mode switching doors 18, 19, and 20 are provided on the airflowupstream side of the individual apertures 14, 15, and 17, respectively.Drive means such as a servomotor, or a manual operation opens and closesthese blow mode switching doors 18, 19, and 20.

Generally, since a large airflow is required in a face mode where theair is blown out from the face aperture 14 for the vehicleair-conditioning apparatus, a draft resistance (a pressure loss) for theface mode is smaller than that for the other blow modes (a foot mode forblowing out the air from the foot aperture 15, and a defroster mode forblowing out the air from the defroster aperture 17).

The blower 7 is a centrifugal blower which draws in air parallel to thedirection of a rotational shaft and blows it away from the shaft in aradial direction (perpendicular to the rotational shaft). A centrifugalmulti-blade fan 72 (abbreviated as a fan hereafter) is made of resin(polypropylene in the present embodiment) or other plastic or metal, andhas a large number of blades 71 about a rotational shaft. A boss 71 a ispresent for holding the multiple blades 71.

In the present embodiment, the fan 72 is a radial fan where a fan outletopening angle (β2) of the blade 71 is more than 60°, and less than 120°,and the specification of the fan 72 is set such that the ratio of theblade length L of the blade 71 (see FIG. 3) to the diameter D of the fan72 (see FIG. 2) (L/D) is 0.12 and higher (L/D=0.14 in the presentembodiment).

The fan outlet opening angle β2 is an angle between the tangent line ofthe blade 71 and the tangent line of an outside edge of the fan 72, andis measured on a forward side of the rotational direction of the fan 72as shown in FIG. 3. The blade length L of the blade 71 is a differencebetween the outside radius and the inside radius of the fan 72.

An electric motor 73 is driven to rotate the fan 72 in FIG. 2. A scrollcasing 74 (abbreviated as a casing hereafter) stores the fan 72, andconstitutes an airflow passage 74 a for circulating the air blown outfrom the fan 72.

As shown in FIGS. 4 and 5, the casing 74 is made of resin (polypropylenein the present embodiment), and is made in a scroll shape about therotational shaft of the fan 72 such that an outer peripheral radius r1increases as a logarithmic spiral function of a scroll angle θ. Anoutlet opening 74 b is formed in a part on the airflow downstream of ascroll end in the casing 74 for connecting with the air conditionercasing 2.

The logarithmic spiral is represented as Equation 1 described below, andan expansion angle n is from 3.5° to 4.5° or from 3.3° to 4.8° (4° inthe present embodiment).

r1=r0·e ^((π/180)·n·θ)  (Equation 1)

In this equation, θ is an angle in radians measured from a base lineconnecting the center of the curvature radius of a nose 74 c with therotational center of the fan 72 in the rotational direction of the fan,and ro is the outer peripheral inner radius on the base line (θ=0).

The nose 74 c is a part where a scroll start side and a scroll end sideoverlap in the casing 74. A part of the airflow downstream side, and apart of the airflow upstream side communicate with each other through aslight gap (not shown) in the nose 74 c.

An inlet opening 75 for introducing the air into the casing 74 opens onthe opposite side of the motor 73 in the rotational axial direction onthe casing 74 as shown in FIG. 2. A bellmouth 76 is formed on anopening-outer edge of the inlet opening 75.

In a section including the rotational shaft, a circular shroud 77 has ashape along the airflow which changes direction from the inlet opening75 toward the outside in the radial direction (perpendicular to theshaft), and is formed on an end of the blades 71 on the side of theinlet opening 75. An opposing bent wall 78 is formed on the casing 74near the bellmouth 76, opposite to the shroud 77 with a predeterminedgap 77 a, and smoothly bends from the bellmouth 76 toward the outside inthe radial direction along the shape of the shroud 77.

In the airflow passage 74 a of the casing 74, the inner radius of theouter periphery r1 increases as a logarithmic spiral such that the flowpassage cross-sectional area in the airflow downstream side (the side ofthe outlet opening 74) is larger than that in the airflow upstream side(the side of the nose 74 c in the casing 74). Simultaneously, expandedparts 74 d and 74 e expanded in the direction parallel with therotational shaft are provided to gradually increase the flow passagecross-sectional area as shown in FIG. 2.

A dimension H1 of the winding-end portion parallel with the rotationalshaft is from 1.3 times to 2.1 times, or from 1.1 times to 2.3 times(1.5 times in the present embodiment) a dimension H0 of the nose 74 c(at scroll angle θ=0) parallel with the rotational shaft. An expandeddimension Hup on the side of the inlet opening 75 is less than 0.4 timesan expanded dimension HLR on the opposite side of the inlet opening 75(0<Hup/HLR<0.4) in the expanded parts 74 d and 74 e.

The expanded dimension Hup on the side of the inlet opening 75 is adimension from the inner wall on the side of the inlet opening 75 to aninner wall of an upper side expanded part in the casing 74 measuredparallel with the rotational shaft as shown in FIG. 2. The upper sideexpanded part is a part of the casing 74 on the scroll end side shiftedby the outer diameter dimension D of the fan 72 from a partcorresponding to the rotational center (the rotation shaft) of the fan72 toward the outlet opening 74 b as shown in FIG. 4.

The expanded dimension HLR on the opposite side of the inlet opening 75is a dimension from the inner wall on the opposite side of the inletopening 75 to an inner wall of a lower (far) side expanded part in thecasing 74 measured parallel to (along) the rotational shaft. The lowerside expanded part is a part of the casing 74 on the scroll end sideshifted by the outer diameter dimension D of the fan 72 from the partcorresponding to the rotation center (the rotation shaft) of the fan 72to the outlet opening 74 b.

The expanded part 74 d out of the expanded parts 74 d and 74 e of thepresent embodiment expands the flow passage cross-sectional area on theside of the inlet opening 75, and is formed proximate the scroll endtoward the outlet opening 74 b of the casing 74. The expanded part 74 eout of the expanded parts 74 d and 74 e expands the flow passagecross-sectional area on the opposite side of the inlet opening 75, andis formed from a range of a part up to about 60° from a neighborhood ofthe nose 74 c in the rotational direction of the fan 72 toward theoutlet opening 74 b of the casing 74.

The following section describes characteristics (actions and effects) ofthe present embodiment. As described above in the summary of theinvention, when the quantity of the airflow blown out from the fan 72 isrelatively small, the quantity of the airflow is not enough for airwhich has collided with a wall surface 74 f to flow along a wall surface74 g, and the tilted surface 74 h. Particularly, the flow does not moveacross or over the entire expanded part 74 e, and a stable swirling flowis not generated.

The air taken into the fan 72 flows into gaps between blades 71 from adirection tilted with respect to the height direction (the directionparallel with the rotational shaft) of the blades 71, and is blown outfrom the fan 72 as shown in FIGS. 6A and 6B.

Since the blade 71 does not add momentum to the airflow parallel to therotational shaft between the blades 71, the air between the blades 71has a constant velocity component in the rotational shaft direction.When the blade length L of the blade 71 increases (L1>L2), because atime required for air flowing out from the gap between the blades 71after flowing thereinto increases, a travel distance of the air betweenthe blades 71 in the rotational shaft direction increases (h1>h0).

When it is assumed that the airflow quantity blown out from the fan 72is constant regardless of the blade length L, the flow rate of the airblown out from the fan 72 increases as the blade length L of the blade71 increases. Thus, increasing the blade length L prevents a decrease ofthe flow rate of the air blown out from the fan 72 when the blown airquantity is small. As a result, the flow extends over the expanded part74 e, a stable swirling flow is generated, and wind noise is reduced.

Since the airflow passage 74 a curves in a scroll shape, when the airflows along the airflow passage 74 a, a secondary flow (a swirling flow)is generated as shown in FIG. 7. Since the swirling flow of the airblown out from the fan 72 matches this secondary flow (the swirlingflow), the swirling flow is more stably generated, and wind noise isreduced.

When the inventors measured the specific noise level using the ratio ofthe blade length L of the blade 71 to the diameter D of the fan 72(L/D), the expansion angle n of the scroll and the expanding ratio inthe axial direction (winding end portion with respect to the dimensionH0 parallel to the rotational axis and nose portion 74 c within casing74, and the dimension H1 (ratio H1/H0) which is parallel to therotational axis) as parameters, the results as shown in FIG. 8 and FIG.9 have been obtained.

FIG. 8 and FIG. 9 respectively show results when the cross-sectionalarea of the scroll air passage with respect to the winding directionangle θ are set as equal, but the expansion angle n and the expandingratio in the axial direction are varied. Therefore, when the expansionangle n is large and the expansion ratio in the axial direction is 1.0,the cross-sectional shape of the air passage 74 a becomes oblong in thehorizontal direction (perpendicular to the rotational shaft). To thecontrary, when the expansion angle n is small, the expansion ratio inthe axial direction becomes larger and the cross-sectional shape of theair passage 74 a becomes oblong in the vertical direction (parallel tothe rotational shaft).

As clearly shown by the test results, when L/D is set to 0.12 and over,the expansion angle n is set to 3.3° and over and 4.8° and below, so thewind noise can be reduced.

As in the first embodiment, when the expansion angle n=4° and theexpansion ratio in the axial direction is 1.5, the ratio ofcross-section of air passage 74 a in length and breadth becomesapproximately 2:1, which is a favorable shape in terms of a pair ofswirling movement of the air flow situated above and below each other.Therefore, the airflow becomes stable and the wind noise can be greatlyreduced.

On the other hand, when the expansion angle n is larger) (n>4.8°, thedistance from the fan 72 to the wall surface 74 g (the outer peripheralside inner wall of the casing 74) becomes larger. Therefore, when theairflow amount is small, as in the foot mode, the momentum of air blownout from the fan 72 becomes small when it collides with the wall surface74 g. As a result, swirling airflow is hardly generated. Also, when theexpansion angle n is larger, the momentum of air blown out from the fan72 becomes larger and swirling airflow is generated by making the bladelength longer. However, since the cross-sectional shape of the airpassage becomes oblong in the horizontal direction, there is not enoughspace for swirling movement. As a result, airflow becomes unstable andthe noise cannot be reduced so much.

To the contrary, when the expansion angle n is smaller) (n<3.3°, thecross-sectional shape of the airflow passage 74 a becomes oblong in thevertical direction. Therefore, when the airflow amount is small, as inthe foot mode, the airflow does not reach the wall surface 74 g andstable swirling airflow is not generated. Also, even though theexpansion angle n is small, the air reaches the wall surface 74 g bylengthening the blade length. However, the swirling airflow becomesoblong in the vertical direction and the airflow becomes unstable.

FIG. 10 shows a test result with a ratio of the dimension H1 to thedimension H0 (H1/H0) as a parameter, where H1 is the dimension of thewinding-end portion parallel with the rotational shaft, and H0 is thedimension of the nose 74 c parallel with the rotational shaft in thecasing 74. As the test results clearly show, when H1/H0 is 1.3 to 2.1,the specific noise level can be reduced. Here, FIG. 10 shows the testresult when L/D=0.14 and the expansion angle n=4.0°.

The definition of the specific noise level follows JIS B 0132, and thetest method is based on JIS B 8340.

In the present embodiment, L/D is set to 0.12 and over, the expansionangle n is set to from 3.5° to 4.5°, and H1/H0 is set from 1.3 to 2.1.However, the present embodiment is not limited to these conditions. Itis only necessary to set L/D to 0.12 and over and to set the expansionangle n from 3.5° to 4.5°, or to set L/D to 0.12 and over, and to setH1/H0 from 1.3 to 2.1.

Second Embodiment

The cross-section of the flow passage 74 a can be set as anapproximately rectangular shape whose corners are arcs in a secondembodiment as shown in FIG. 11. With this structure, since an unstableswirling flow is prevented from being generated at the corners of theairflow passage 74 a, and simultaneously, a generated swirling flow issmoothly circulated, the swirling flow is stabilized, and wind noise isreduced. It is preferable that the curvature radius of the arcs isproperly set according to the radius of the swirling flow generated inthe airflow passage 74 a.

Third Embodiment

FIG. 12 shows a third embodiment of the present invention. A protrusion74 j protruding toward the fan 72 is formed along almost the entireairflow passage 74 a on the inner wall of the outer peripheral portionof the casing 74, and the cross-section of the protrusion 74 j isapproximately triangular (wedge-shaped) and protrudes toward the fan 72when the protrusion 74 j is seen from a primary flow direction of theair flowing through the airflow passage 74 a.

With this structure, since the protrusion 74 j is provided at a partwith which air with the highest flow rate of the air blown out from thefan 72 collides, the air blown out from the fan 72 is easily dividedinto the side of the inlet opening 75 and the opposite side. Thispromotes the generation of swirling flow to reduce wind noisegeneration.

Fourth Embodiment

In the present embodiment, the blade length L is extended to shift theair blown out from the fan 72 toward the opposite side of the inletopening 75 for increasing the flow rate. Also, the air blown out fromthe fan 72 collides with the wall surface 74 f to generate a stableswirling flow as described above. In a fourth embodiment, L/D is set to0.12 and over, a fan inlet opening angle β1 is set from 55° to 85°, afan outlet opening angle β2 is set from 15° to 45°, and a fan advancingangle γ is set to 4° to 10°. With these settings, the air is preventedfrom separating from the blades 71 and from between the blades 71. Also,air counter-flow is prevented from forming between the blades 71 at theoutlet opening side of the fan, and wind noise is reduced.

With reference to FIG. 13, the fan inlet opening angle β1 is an anglebetween the tangent line of the blade 71 and the tangent line of aninside edge of the fan 72, and is measured on the forward-facing side ofthe blade in the rotational direction of the fan 72 as shown in FIG. 13.The fan advancing angle γ is an angle between a line L1 connecting anend of the blade 71 closest to an inlet opening side with the rotationalcenter of the fan 72 and a line L2 connecting an end of the blade 71near an outlet opening side with the rotation center of the fan 72. Thatis, line L1 is drawn from the rotational center of the fan 72 tangent toa first end of the blade 71 that is closest to the rotational center.This first point of tangency is on the front side of the blade thatleads during the rotation of the blade 71. The line L2 is drawn from therotational center of the fan 72 tangent to a second end of the blade 71farthest from the rotational center. This second point of tangency is onthe front side of the blade 71 that leads during the rotation of theblade 71.

The following section describes characteristics (actions and effects) ofthe present embodiment.

FIG. 14A shows a state of the air flowing between the blades 71 when thefan inlet opening angle β1 is large (about 90°). When the fan inletopening angle β1 is larger than an angle at which the air flows into thefan 72 (theoretical flow-in angle is about 30°), the air between theblades 71 is separated from the blade 71 on the forward side in therotational direction. Thus, a flow rate distribution on the fan outletopening side becomes uneven, and noise tends to be generated.

FIG. 14B shows a state of the air flowing between the blades 71 when thefan inlet opening angle β1 is set to the theoretical flow-in angle. Inthis state, though, the separation of the air from the blade 71 on theforward side in the rotation direction is prevented on the inlet openingside. However, when the fan advancing angle γ is small, the airseparated from the blade 71 on the forward side in the rotationdirection is blown out without being attached to the blade 71 again onthe outlet opening side. As a result, a counter-flow is generated on theforward side in the rotation direction, and new noise may be generated.

In the present embodiment, L/D, the fan inlet opening angle β1, the fanoutlet opening angle β2, and the fan advancing angle γ are set to propervalues, and the separation on the inlet opening side is restrained, andsimultaneously, the air separated from the blade 71 on the forward sidein the rotational direction is attached again as shown in FIGS. 15A and15B. As a result, the airflow between the blades 71 is optimized, astable swirling flow is generated, and noise is reduced.

FIG. 16 represents a test result showing a relationship between L/D andthe minimum specific noise level, and a relationship between L/D and theairflow rate. FIG. 17 represents a test result showing a relationshipbetween the fan inlet opening angle β1 and the specific noise level, anda relationship between the fan inlet opening angle β1 and the airflowrate. FIG. 18 represents a test result showing a relationship betweenthe fan outlet opening angle β2 and the specific noise level, and arelationship between the fan outlet opening angle β2 and the airflowrate. FIG. 19 represents a test result showing a relationship betweenthe advancing angle γ and the specific noise level, and a relationshipbetween the advancing angle γ and the airflow rate. The test conditionsand the definitions of the technical terms are the same as those in theembodiments described above.

As these test results clearly show, L/D should be set to 0.12 and over(0.15 in the present embodiment), the fan inlet opening angle β1 shouldbe set to from 55° to 85° (65° in the present embodiment), thefan-outlet-opening angle β2 should be set from 15° to 45° (35° in thepresent embodiment), and the fan advancing angle γ should be set from 4°to 10° (7° in the present embodiment).

In the present embodiment, the curvature radius r1 on the inlet openingside of the blade 71 is equal to or less than the curvature radius r2 onthe outlet opening side of the blade 71, and curved surfaces having morethan two curvature radii r1 and r2 are smoothly connected to form theblade 71 such that the fan inlet opening angle β1, the fan outletopening angle β2, and the fan advancing angle γ satisfy the advantageousconditions described above. However, the present embodiment is notlimited to this construction, and the curvature radius may increasegradually from the inlet opening side to the outlet opening side, or maybe constant as long as the conditions above are satisfied.

The present embodiment may be combined with the embodiments describedabove. As shown in FIGS. 8 and 9, and FIGS. 16 to 19, L/D is set to 0.12and over, the fan inlet opening angle β1 is set from 55° to 85°, the fanoutlet opening angle β2 is set from 15° to 45°, the fan advancing angleγ is set from 4° to 10°, and the expansion angle n is set from 3.3° to4.8°. Alternatively, L/D is set to 0.12 and over, the fan inlet openingangle β1 is set from 55° to 85°, the fan outlet opening angle β2 is setfrom 15° to 45°, the fan advancing angle γ is set from 4° to 10°, andthe expansion angle n is set from 3.5° to 4.5°.

The present embodiment may be applied to a casing not including theexpanded parts 74 d and 74 e (the dimension of the airflow passage 74 aparallel with the rotational shaft is constant).

Other Embodiments

While the tilted surface 74 h is provided in the expanded part 74 e inthe first embodiment, the present invention is not limited to thisconstruction, and the airflow passage may have other shapes such as asimple rectangle, a circle, and an ellipse.

1. A centrifugal blower comprising: a centrifugal multi-blade fan havingmultiple blades about a rotational shaft, wherein said centrifugal fantakes in air along an axial direction of said rotational shaft and blowssaid air outward in a radial direction with respect to said rotationalshaft; and a scroll casing for storing said centrifugal multi-blade fan,said scroll casing defining a scroll-shaped airflow passage fordirecting said air blown out from said centrifugal multi-blade fan, saidscroll casing having an intake opening at a first end of said rotationalshaft and an outlet opening at a scroll end at an airflow downstreamportion; wherein a first expanded part and a second expanded part areexpanded in a direction parallel with said rotational shaft and areprovided in said airflow passage such that a flow passagecross-sectional area on the airflow downstream side is larger than thaton an airflow upstream side; a ratio of a blade length of said blades toa diameter of the centrifugal multi-blade fan is equal to or over 0.12;an outer peripheral radius of said scroll casing expands as alogarithmic spiral, and its expansion angle is from 3.3° to 4.8°; afirst expanded part expands the flow passage cross-sectional area on theside of the inlet opening and is formed proximate the scroll end towardthe outlet opening; and the second expanded part expands the flowpassage cross-sectional area on the opposite side of the inlet openingand is formed from a range of a part up to about 60° from a neighborhoodof the nose in the rotational direction of the fan toward the outletopening.
 2. The centrifugal blower according to claim 1, wherein adimension of said scroll end portion in a direction parallel with saidrotational shaft is from 1.1 times to 2.3 times a dimension of a nose insaid scroll casing in a direction parallel with said rotational shaft.3. The centrifugal blower according to claim 1, wherein a dimension ofsaid scroll end portion in a direction parallel with said rotationalshaft is from 1.3 times to 2.1 times of a dimension of a nose in saidscroll casing in a direction parallel with said rotational shaft.
 4. Thecentrifugal blower according to claim 1, wherein said airflow passagehas an approximately rectangular cross-section.
 5. The centrifugalblower according to claim 1, wherein said airflow passage has anapproximately rectangular cross-section with rounded interior passagecorners.
 6. The centrifugal blower according to claim 1, wherein aprotrusion protruding toward said centrifugal multi-blade fan isprovided on an inner wall on an outer peripheral side of said scrollcasing, and has an approximately triangular shape protruding toward saidcentrifugal multi-blade fan when viewed from a primary flow direction ofthe air flowing through said airflow passage.
 7. A centrifugal blowercomprising: a centrifugal multi-blade fan having multiple blades about arotational shaft, wherein said centrifugal fan takes in air along anaxial direction of said rotational shaft and blows said air outward in aradial direction with respect to said rotational shaft; and a scrollcasing for storing said centrifugal multi-blade fan, said scroll casingdefining a scroll-shaped airflow passage for directing said air blownout from said centrifugal multi-blade fan, said scroll casing having anintake opening at a first end of said rotational shaft and an outletopening at a scroll end at an airflow downstream portion, wherein: afirst expanded part and a second expanded part are expanded in adirection parallel with said rotational shaft and are provided in saidairflow passage such that a flow passage cross-sectional area on theairflow downstream side is larger than that on an airflow upstream side;a ratio of a blade length of said blades to a diameter of thecentrifugal multi-blade fan is equal to or over 0.12; an outerperipheral radius of said scroll casing expands as a logarithmic spiral,and its expansion angle is from 3.3° to 4.8°; and an expanded dimension(Hup) on the side of the inlet opening is less than 0.4 times anexpanded dimension (HLR) on the opposite side of the inlet opening inthe first and second expanded parts.
 8. The centrifugal blower accordingto claim 7, wherein a dimension of said scroll end portion in adirection parallel with said rotational shaft is from 1.1 times to 2.3times a dimension of a nose in said scroll casing in a directionparallel with said rotational shaft.
 9. The centrifugal blower accordingto claim 7, wherein a dimension of said scroll end portion in adirection parallel with said rotational shaft is from 1.3 times to 2.1times of a dimension of a nose in said scroll casing in a directionparallel with said rotational shaft.
 10. The centrifugal bloweraccording to claim 7, wherein said airflow passage has an approximatelyrectangular cross-section.
 11. The centrifugal blower according to claim7, wherein said airflow passage has an approximately rectangularcross-section with rounded interior passage corners.
 12. The centrifugalblower according to claim 7, wherein a protrusion protruding toward saidcentrifugal multi-blade fan is provided on an inner wall on an outerperipheral side of said scroll casing, and has an approximatelytriangular shape protruding toward said centrifugal multi-blade fan whenviewed from a primary flow direction of the air flowing through saidairflow passage.